1. Field of the Invention
The present invention relates to a hydrogen production apparatus, in which hydrogen is produced by the electrolysis of water.
2. Description of the Related Art
As shown in FIG. 1, there has conventionally been known a hydrogen production apparatus 1 comprising a plurality of single cells 7, 7 being stacked on each other, in which each of the single cells 7, 7 comprises a solid polymer electrolyte membrane 2, power feeders 3, 4 provided opposed to each other on a cathode side and an anode side of the electrolyte 2 respectively, and separators 5, 6 stacked on the respective power feeders 3, 4. Each side of the solid polymer electrolyte membrane 2 comprises a catalyst electrode which is not shown in FIG. 1.
The above described single cells 7, 7 are sandwiched between end plates 14, 14, and are securely fixed to the end plates 14, 14 by screwing a bolt 15 which has been inserted through the end plates 14, 14 into a nut 16. As a result, each of the power feeders 3, 4 and each of the separators 5, 6 are pressed against the solid polymer electrolyte membrane 2.
In the hydrogen production apparatus 1, as shown in FIG. 2(a), each of the above described separators 5, 6 comprises in a peripheral portion thereof a pressure contact surface 17 to be pressed against the solid polymer electrolyte membrane 2, together with a recess portion 18, which is positioned inwardly of and surrounded by the pressure contact surface 17, wherein the power feeders 3, 4 are disposed within the recessed portion 18. The separators 5, 6 also comprise fluid channels 8, 10 respectively, to which the power feeders 3, 4 are exposed. The power feeders 3, 4 are porous bodies, and a current is applied through the separators 5, 6 by the use of current-carrying means which is not shown in this figure.
In the hydrogen production apparatus 1 which is in a state that each of the power feeders 3, 4 and each of the separators 5, 6 are pressed against the solid polymer electrolyte membrane 2, once water is supplied to the fluid channel 10 of the anode side separator 6 while applying a current to the power feeders 3, 4, water which has been supplied to the fluid channel 10 is electrolyzed at the catalyst electrode layer provided on the anode side, and then hydrogen ions, electrons, and oxygen gas are generated. The hydrogen ions being accompanied by water molecules pass through the solid polymer electrolyte membrane 2 and move toward the cathode side, and then receive electrons from a catalyst electrode layer provided on the cathode side to generate hydrogen gas. The hydrogen gas passes through the porous power feeder 3, and then moves into the fluid channel 8 of the separator 5. Consequently, the hydrogen production apparatus 1 can obtain hydrogen within the fluid channel 8 on the cathode side.
As the above described power feeders 3, 4 used for the hydrogen production apparatus 1, it has been known a feeder having rigidity such as a porous body obtained by sintering spherical titanium particles (see Japanese Patent Laid-Open No. 2004-71456, for example).
When the above described rigid feeder is used as the power feeders 3, 4, a thickness of each of the power feeders 3, 4 is adapted to correspond to a depth of the recess portion 18 of each of the separators 5, 6 as shown in FIG. 4(a) so that surfaces 3a, 4a of the power feeders 3, 4 become flush with the pressure contact surfaces 17 of the separators 5, 6 respectively. This is because that, if a thickness of each of the power feeders 3, 4 is greater than a thickness of the recess portion 18 of each of the separators 5, 6, the power feeder 3 protrudes from the recess portion 18 and the surface 3a of the power feeder 3 extends to an outside of the pressure contact surface 17 of the separator 5 as shown in FIG. 4(b) for example, and consequently, hydrogen gas which has been generated on the cathode side leaks from a gap S between a surface of the solid polymer electrolyte membrane 2 and the pressure contact surface 17 of the separator 5.
However, the provision of the power feeders 3, 4 whose surfaces 3a, 4a are flush with the pressure contact surfaces 17 of the separators 5, 6 has a disadvantage that both the power feeders 3, 4 and the separators 5, 6 are required to be processed with a high degree of precision and thus are hard to be manufactured. Although it is conceivable that the surfaces 3a, 4a of the power feeders 3, 4 can be flush with the pressure contact surfaces 17 of the separators 5, 6 by grinding the protruding portions if the power feeders 3, 4 protrude from the recess portions 18, an electrolytic efficiency in this case is decreased since porous portions of the porous power feeders 3, 4 are occluded, and hydrogen ions and hydrogen gas and the like are prevented from moving.
In addition, the provision of the power feeders 3, 4 whose surfaces 3a, 4a are flush with the pressure contact surfaces 17 of the separators 5, 6 has a disadvantage that the moisture retention is decreased, because the solid polymer electrolyte membrane 2 is uniformly compressed when each of the power feeders 3, 4 and the pressure contact surface 17 of each of the separators 5, 6 are pressed against the solid polymer electrolyte membrane 2. Since hydrogen ions which have been generated on the anode side of the solid polymer electrolyte membrane 2 pass into the cathode side together with water molecules as described above, the passage of the hydrogen ions is inhibited when the moisture retention of the solid polymer electrolyte membrane 2 is decreased and consequently the electrolytic efficiency is decreased.